数据结构 之 '链表'

链表

链表是一种物理存储单元上非连续、非顺序的存储结构，数据元素的逻辑顺序是经过链表中的指针连接次序实现的。链表由一系列结点（链表中每个元素称为结点）组成，结点能够在运行时动态生成。每一个结点包括两个部分：一个是存储数据元素的数据域，另外一个是存储下一个结点地址的指针域。 相比于线性表顺序结构，操做复杂。因为没必要须按顺序存储，链表在插入的时候能够达到O(1)的复杂度，比另外一种线性表顺序表快得多，可是查找一个节点或者访问特定编号的节点则须要O(n)的时间，而线性表和顺序表相应的时间复杂度分别是O(logn)和O(1)。

基本操做

class Node(object):
    """
    封装节点
    """
    def __init__(self, item):
        # 存储数据元素的数据域
        self.item = item

        # 存储下一个结点地址的指针域
        self.next = None


class Link(object):
    """
    封装链表
    """
    def __init__(self):
        # 初始化一个空链表
        self._head = None
        # '_head' 用于指向链表的第一个节点

    def add(self, item):
        """
        链表首部插入节点
        :param item:
        :return:
        """
        node = Node(item)
        node.next = self._head
        self._head = node

    def travel(self):
        """
        遍历每个节点
        :return:
        """
        cur = self._head
        while cur:
            print(cur.item)
            cur = cur.next

    def length(self):
        """
        链表中节点的个数
        :return:
        """
        count_node = 0
        cur = self._head
        while cur:
            count_node += 1
            cur = cur.next
        return count_node

    def isEmpty(self):
        """
        判断链表是否为空
        :return:
        """
        return self._head == None

    def search(self, item):
        """
        查找是否存在item对应的节点
        :param item:
        :return:
        """
        find = False
        cur = self._head
        while cur:
            if cur.item == item:
                find = True
                break
            else:
                cur = cur.next
        return find

    def append(self, item):
        """
        链表的尾部插入节点
        :param item:
        :return:
        """
        node = Node(item)
        if self._head == None:
            self._head = node
            return

        cur = self._head
        pre = None
        while cur:
            pre = cur
            cur = cur.next
        pre.next = node

    def insert(self, pos, item):
        """
        链表中指定的位置插入新的节点
        :param pos:
        :param item:
        :return:
        """
        node = Node(item)
        if pos == 0:
            node.next = self._head
            self._head = node
            return
        pre = None
        cur = self._head
        for i in range(pos):
            pre = cur
            cur = cur.next
        pre.next = node
        node.next = cur

    def remove(self, item):
        """
        删除节点
        :param item: 
        :return: 
        """
        cur = self._head
        pre = None

        if cur.item == item:
            self._head = cur.next
            return
        while True:
            pre = cur
            cur = cur.next
            if cur.item == item:
                pre.next = cur.next
                break
            if cur == None:
                break

    def reverse(self):
        """
        链表倒置
        :return: 
        """
        pre = None
        cur = self._head
        next_node = cur.next

        while cur:
            cur.next = pre
            pre = cur
            cur = next_node
            if cur != None:
                next_node = next_node.next
        self._head = pre
        self.travel()


if __name__ == '__main__':
    link = Link()
    link.append(1)
    link.append(2)
    link.append(3)
    link.append(4)
    link.reverse()
    

# 4
# 3
# 2
# 1